1. Field of the Invention
The present invention relates to a lens barrel drive apparatus which causes a lens barrel holding an optical component for an image pickup apparatus to move along an optical axis at the time of focusing or zooming.
2. Description of the Related Art
Conventionally, there has been proposed a lens barrel drive apparatus which causes a lens of a still camera, a video camera, or the like to move along the optical axis (see e.g. Japanese Laid-Open Utility Model Publication (Kokai) No. H02-71155) . In this conventional lens barrel drive apparatus, a small stepping motor is disposed in parallel with a lens to drive the lens via a lead screw or the like.
The stepping motor used for the lens barrel drive apparatus of this type has a solid cylindrical shape with no opening (in the central part, no through opening is formed but a component part is provided). Thus, in order to prevent interference with an optical path, the stepping motor has to be disposed outside the lens, it is difficult to make the entire lens barrel drive apparatus small in diameter.
In view of the foregoing, there has been proposed a lens barrel drive apparatus which uses a hollow cylindrical motor and uses an opening penetrating through the central part of the motor as the optical axis of the lens so as to make the radial size of the apparatus small (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-051524 and U.S. Pat. No. 4,605,286). Such an arrangement can reduce the size of the lens barrel drive apparatus. A description will now be given of the conventional lens barrel drive apparatuses with reference to FIGS. 19A and 19B.
FIG. 19A is a front view of the conventional lens barrel drive apparatus as viewed in the direction of the optical axis in the case where the solid motor is used. FIG. 19B is a front view of the conventional lens barrel drive apparatus as viewed in the direction of the optical axis in the case where the hollow motor is used.
In the case where the solid motor M1 is used as shown in FIG. 19A, the diameter of the lens barrel drive apparatus is expressed by the following equation, (the diameter of lens L1)+2×(thickness of lens barrel H1)+2×(diameter of solid motor M1). On the other hand, in the case where the hollow motor M2 is used as shown in FIG. 19B, the diameter of the lens barrel drive apparatus is expressed by the following equation, (the diameter of lens L2)+2×(thickness of lens barrel H2)+2×(thickness the diameter of hollow motor M2) . The thickness of the hollow motor is approximately equal to the radius of the solid motor. Thus, using the hollow motor can reduce the size of the lens barrel drive apparatus by the diameter of the solid motor.
There has been conventionally proposed another lens barrel drive apparatus which uses a hollow motor to drive a lens barrel supported by guide bars (see e.g. Japanese Laid-Open Patent Publication (Kokai) Nos. 2004-347890 and 2005-202316). In the lens barrel drive apparatus of this type, the lens barrel can be held with high accuracy, low friction, and low noise since the guide bars support the lens barrel.
However, the above other conventional lens barrel drive apparatus have the problem that, since the hollow motor drives the lens barrel supported by the guide bars, it is difficult to make the lens barrel drive apparatus small in diameter. This will be described with reference to FIGS. 20A and 20B.
FIG. 20A is a front view of the other conventional lens barrel drive apparatus as viewed in the direction of the optical axis in a case where the guide bars are disposed inside the hollow motor, and FIG. 20B is a front view of the other conventional lens barrel drive apparatus as viewed in the direction of the optical axis in a case where the guide bars are disposed in notches of the hollow motor.
As shown in FIG. 20A, since the guide bars B3 are disposed at both ends of a lens L3 which is circular, the hollow motor M3 has to be disposed further outside the guide bars B3. For this reason, there is a dead space between the lens barrel H3 and the hollow motor M3, and it is difficult to make the lens barrel drive apparatus small in size and diameter. To address this problem, notches are formed in the hollow motor M4, and guide bars B4 are disposed in the notches as shown in FIG. 20B. This arrangement can inhibit the formation of a dead space between the lens barrel H4 and the hollow motor M4 and reduce the diameter of the lens barrel drive apparatus.
If the hollow motor of which rotor is a magnet is used as is in case of the above conventional lens barrel drive apparatus, notches for preventing interference with the guide bars and the lens barrel cannot be formed in the rotary magnet. Thus, the thick magnet has to be disposed outside the guide bars, and it is difficult to make the lens barrel drive apparatus small.
Also, in the above other conventional lens barrel drive apparatus, a bearing of the motor is notched so as to reduce the size of the lens barrel drive apparatus. However, since a magnet and a coil are disposed outside the guide bars, there is a limit to the extent to which the lens barrel drive apparatus can be reduced in diameter.